Process for the extraction of aromatic hydrocarbons in admixture with paraffinic and naphthenic hydrocarbons by means of a selective solvent



8, 1966 a. coussERANs 3, 84,528

PROCESS FOR THE EXTRACTION OF AROMATIC HYDROCARBONS IN ADMIXTURE WITH PARAFFINIC AND NAPHTHENIC HYDROCARBONS BY MEANS OF A SELECTIVE SOLVENT Filed Oct. 2, 1962 5 Sheets-Sheet 1 FIG FIG 2 i/berf Cousserans INVENTOR JIM, BY

ATTORNEYS Nov. 8, 1966 e. COUSSERANS 3,284,528

PROCESS FOR THE EXTRACTION OF AROMATIOHYDROCARBONS IN ADMIXTURE WITH PARAFFINIC AND NAPHTHENIC HYDROCARBONS BY MEANS OF A SELECTIVE SOLVENT Filed Oct. 2, 1962 5 Sheets-Sheet 2 2 "m WASHING COLUMN & f 6\ DISTILLATION COLUMN a FEED l7 T A'W ''23 t COOLER 3 SZIIORAGE TANK K 22 k P 9 mtk J n; U

Gl/arf swans INVENTOR MM,

F/G a BY $4 M ATTORNEYS Nov. 8, 1966 G. coussERANs 3,284,528

PROCESS FOR THE EXTRACTION OF AROMATIC HYDROCARBONS IN ADMIXTURE WITH PARAFFINIC AND NAPHTHENIC HYDROCAHBONS BY MEANS OF A SELECTIVE SOLVENT Filed Oct. 2, 1962 5 Sheets-Sheet 5 SETTLING 3 TANK 2.51 Dlil'cllclagllqoN ff- CONDENSER r A (f (a 8 5 )U; Egrglfsl'awu DECATPATI'SXPIIONI/ 25 f g, 1 a 55 /8 20 I coouzn STORAGE TANK ' INVENTOR F76 4 BY 5M1 ATTORNEYS United States Patent PRQCESS FOR THE EXTRACTION OF AROMATIC HYDROCARBONS KN ADMIXTURE WITH PAR- AFFHNEC AND NAPHTHENIC HYDROCARBGNS BY MEANS UP A SELECTIVE SOLVENT Gilbert Cousserans, Toulouse, Haute Garonne, France, assignor to @fice National Industriel de lAzote, Haute Garonne, France, a corporation of France Filed Get. 2, 1962, Ser. No. 227,875 Claims priority, application France, Oct. 5, 1961, 4,740 4 Claims. (Cl. 260-674) This invention relates to the separation of aromatic hydrocarbon components from their mixtures with aliphatic and occasionally naphthenic hydrocarbons by solvent extraction methods. More particularly, the invention concerns a solvent extraction process utilizing, as a solvent medium, water mixtures of the esters of carbamic and/ or thiocarbamic acids.

The increased consumption of high octane gasolines and pure aromatic products for the chemical synthesis industries has stimulated a new branch of petrochemistry, aimed at producing aromatic hydrocarbon fractions from feed stock rich in both aromatics and aliphatics. Because of the similarity of boiling points among the various components of aromatic-aliphatic mixtures obtained from, for example, catalytic reforming, expensive fractional distillation equipment is necessary to effect a sepparation. More recently, liquid-liquid extraction techniques have been investigated as a means of separating the aromatic components from the aliphatic. Such techniques have proved of such value that they are replacing fractional distillation, since they are both effective and inexpensive.

Several prior art solvent extraction processes have been developed, but they all have inherent disadvantages which lead to costly operation and inefficient separations, Several processes utilize as selective solvents diand monoethylene glycols as Well as sulfolane (tetramethylene sulfone), the monoethylene glycol generally being mixed with large percentages of methanol, the diethylene glycol being used alone or with water. The process, described in Chemical Engineering Progress, vol. 54, No. 8, August 1958, is one such process. Certain inherent disadvantages make such a process undesirable. One and the same solvent cannot at the same time resolve large quantities of aromatic hydrocarbons and still be very selective. If it dissolves them in large proportions, the quantities of solvent involved will be smaller. But, assuming that its selectivityratio of co-eflicients of average separation of aromatic and non aromatic hydrocarbons-is reduced, it is necessary to enrich the extract by employing a larger number of stages for Washing the latter, while returning a fraction of the extract by direct reflux or by the use of an anti-solvent, or even by using a secondary solvent which latter involves the necessity of ultimately separating the secondary solvent from the raffinate.

Also prior art processes have utilized various carbamate salts, particularly methylethyl ammonium methylethyl carbarnate, as solvents. For example, Lindahl, U.S. 2,963,428, utilizes the aforementioned carbamate as well as other N-substituted alkyl carbamates such as the methyl-methyl compound, the ethyl-ethyl compound and the diethyl-diethyl compound, along with higher molecular weight derivatives such as l-propyl and n-ocyl compounds. However, lack of stability of such compounds makes them unsuitable for use as solvents. In addition, Beinfest et al. U.S. 3,014,807, proposes the use of mixtures of alkyl carbamates, such as ethyl and methyl carbamates, in a eutectic composition as solvents for aromatics. Beinfest contemplates binary, ternary and quaternary mixtures as well as other multicornponent mixtures,

The ideal solvent for an extraction process of the invention should conform to many requirements. It should be stable and chemically inert at normal conditions of use,

it should have a specific gravity and boiling point widely dilferent and higher than that of the aromatics to be extracted, it should have a high selectively with respect to the components to be separated, and it should be readily available in the market at an economical price.

Thus, the primary object of this invention is to provide an improved solvent extraction process, utilizing highly effective solvents.

Another object of this invention is to provide a process for extracting aromatic hydrocarbons from hydrocarbon mixtures, utilizing particular carbamate solvents.

Still another object of this invention is to provide particular carbamic ester solvents which are both chemically inert and stable at the temperatures employed for solvent extraction.

Another object of this invention is to provide particular carbamate solvents which have low solubility in aliphatic hydrocarbons and yet are highly miscible with aromatic hydrocarbons.

Yet a further object of this invention is to provide particular carbamate solvents which have widely diiferent boiling points and specific gravities from aromatic hydrocarbons miscible therewith.

In order to fully understand the invention, reference should be made to FIGURES 1 to 4. FIGURES 1 and 2 are conventional miscibility diagrams, illustrating the phase relationship between the components of the inventive process. FIGS. 3 and 4 are flow diagrams illustrating examples of the inventive extraction system.

In order that the selective extraction of the aromatic hydrocarbons A from their mixture with aliphatic and naphthenic hydrocarbons B be feasible by using but one solvent S, the miscibility diagrams ABS should be of either the type shown in FIG. 1 or FIG. 2. The non-miscibility areas are shaded. Solvents which conform to the diagram of FIG. 2, while meeting in all other respects the requirements set out above, are a mixture of Water and one or more of the components chosen from among esters of carbamic acid and thiocarbamic acid. The general formulae of such compounds are ROCONH (carbamic ester), e.g. CH (CH OCONH and ROCSNH (thiocarbamic ester), e.g. CH OCSNH wherein R represents an alkyl radical of between 1 and 6 carbon atoms.

Three solvents of particular advantage among those listed above are methylcarbamate, ethyl carbarnate and methylthiocarbamate. Such solvents may be used singly or in mixtures with one another. By way of example, the following table sets forth average partition co-efiicients and the average selectivity measured at 50 C. of two solvents constituted respectively by mixtures of 10% of water and of methyl carbamate. The partition -co-eiiicient D=Ca/ Cb where Ca and Cb respective- -ly represent the concentration of solute in the solvent phase and in the hydrocarbon phase.

The high solubility of the aromatic component in the solvents of the invention enables reduction in the volume of solvent circulated and, consequently,

tion. In addition, these solvents being very selective,

POWCT 001181111113 the operation of the process of the invention can be carried out in apparatus of reduced size. Thus, the process according to the invention is effected by a succession of simple operations in an apparatus of smaller size than that required in carrying out the known processes. In addition, the losses of solvent by decomposition or entrainment, burdening the economy of the extraction processes using prior art solvents, are negligible due to the high stability of the inventive carbamic solvents and their very low solubility in the aliphatic and naphthenic hydrocarbons.

The solvents according to the invention also present the advantage of making possible very high speeds of exchange between the existing liquid phases, due to their low viscosity, and of not raising corrosion problems or regeneration problems.

The embodiment of the precess according to the invention is illustrated in the flow diagram of FIG. 3. As an example, the aromatic components of a light fraction of petroleum catalytic reforming (platforming) can be ex tracted by means of a :carbamic or thiocarbamic solvent. Such solvent consists of carbamic esters with water, thiocarbamic esters with water or admixtures of carbamic and thiocarbamic ester with water. The starting petroleum fraction, boiling in a temperature range between 65 and 175 C. and containing about 50% of C6 to C11 aromatic components and 50% of C to C12 non-aromatic components, is passed, through inlet 1, into an extraction column 2 fed with solvent at its upper end 3. The extraction column 2 is internally provided with any conventional means to effect good contact between the liquids present.

The aromatic components are extracted from the starting petroleum fraction and as their solution in the solvent is denser than the aliphatic and naphethenic fractions, they flow down to the lower end of the column.

The :raffinate leaving the upper end of the extraction column 2 is taken by piping 4 and fed into the lower part 5 of a washing column 6 in which the aliphatic and. naphthenic components are separated from the entrained carbamate-water solvent by water washing. The hydrocarbons leave the washing column 6 at its upper end 7 and the aqueous wash solution, containing carbamatewater solvent washed from the hydrocarbons, is injected through piping 8 into the lower part 9 of column 2 in which it acts as an anti-solvent. The extraction column 2 may be provided m'th any conventional means to effect liquid-liquid contact.

The extract containing the carbamate-water solvent and the aromatic components leaves the lower part of the extraction column 10 and is fed through inlet 11 into the distillation column 13 through piping 12. Following distillation, the top fraction, containing the aromatic components and water, is condensed in cooler 15 and passed into a settling tank 16 in which it separates into two layers. The upper layer, which is essentially a mixture Olf extracted hydrocarbons, is sent to storage tank 17 through piping 18, and from there to the final separations of henzene, toluenes and xylenes from each other.

The lower layer in settling tank 16 which is essentially water, is recycled to both columns 13 and 6 at inlets 14 and 19, respectively. The carbamate material, taken from the distillation column 13 through outlet 20, is forwarded into tank 21 from which it is pumped through pump 22 into the extraction column 2 at inlet 3.

The diagram according to FIG. 3 can be modified according to FIG. 4 in order to make possible the production of the very pure aromatic hydrocarbons.

The extract traction containing the solvent, water and aromatic constituents leaves the bottom of the extraction column 2 at 10 and is introduced at 11 into one of the upper plates of the distillation column 13. The fraction at the head of the distillation which contains water, aromatic hydrocarbons and aliphatic and naphthenic hydrocarbons having escaped separation, is condensed in the cooler condenser 15 and is sent to the decantation tank 16 where it separates into two layers. The upper layer containing the hydrocarbons is used to assure reflux in column 13 into which a part is injected at 14, and also to assure reflux in the extraction column 2 into the bottom of which another part of the said hydrocarbons is introduced at 9. The intermediate distillation fraction withdrawn at 23 contains aromatic hydrocarbons of a degree of purity greater than 99.8% and water. After condensation in the cooler condenser 24 and decantation in tank 25, the aromatic hydrocarbons are sent to storage 17. The water coming from tank 25 is combined with that from decantation tank 16 and serves, on the one hand, for washing the aliphatic and naphthenic fraction by recycling at 19 in the washing column 6 and, on the other hand, makes possible entrainment of the hydrocarbons by recycling at 26 into the boiler of the distillation column. In the description according to FIG. 4, the water no longer .plays the role of anti-solvent in extraction column 2, but entrains recovered solvent to the distillation, and facilitates distillation of aliphatic and naphthenic hydrocarbons which have escaped by separation.

It is understood that the drawings are merely diagrammatic and that the elements of the flow diagrams as shown in no way limit the invention.

The following illustrative examples are set forth as presently preferred embodiments of the invention. In these examples, the percentages are by weight.

Example 1 Into an apparatus of the type shown diagrammatically in FIG. 4, there is fed, at the top of the third stage of the extraction column comprising 10 theoretical stages, 10 tons per hour of a petroleum fraction containing by weight 51.5% of aromatics and 48.5% of aliphatics and naphthenics. The solvent employed is methyl carbamate containing 15% of water and the extraction operation is carried out under 4 atmospheres pressure and at a temperature of C. The rafiinate sent to washing then contains 0.41 t./h. of aromatics, 4.85 t./h. of aliphatics and 0.10 t./h. of solvent. Washed in countercurrent with 1.05 t./h. of water, 5.26 t./h. of raffinate are separated from 0.10 t./h. of solvent.

The extract which contains 8.9 t./h. of aromatics and 144.9 t./h. of solvent is sent to distillation at 120 C. The head fraction yields after condensation and decantation 9.05 t./h. of hydrocarbons (66.63 t./h. of aromatics and 2.42 t./h. of aliphatics and naphthenics) of which 5.61 t./h. serve for reflux in the distillation column and 3.44 t./h. for reflux in the extraction column. Intermediate withdrawal from the distillation column yields, after condensation and decantation, 4.74 t./h. of aromatics of 99.9% purity and 0.92 t./h. of water. This water is combined with 1.22 t./h. of water separated from the head fraction and the combination is recycled into the apparatus: 1.05 t./h. go to the washing column and are there charged with 0.10- t./h. of solvent and then combined with 1.09 t./h. of water remaining before being introduced into the boiler of the distillation column. The tail fraction of the latter, which yields t./h. of solvent and 0.72 t./h. of aromatics is injected into the head of the extraction column.

Example 2 In an apparatus of the type shown diagrammatically in FIG. 3 and comprising an extraction column with 8 theoretical plates, there are introduced into the latter at the level of the 2.5 t./h. stage a feed of 10 cubic meter/ hour of the same petroleum fraction as that used in Example 1. The solvent, constituted by a mixture of 95% of methyl thiocarbamate and 5% of water, is introduced into the head of the column at the rate of 95 cubic meters/ hour.

The non-aromatic fraction leaving the extraction column at the top part thereof is introduced into a washing column comprising two theoretical plates and in which it is brought into contact, in countercurrent, with cubic meters/hour of Water. The solvent entrained by the water is recycled into the extraction column where the Water acts as antisolvent.

The extraction yield is about 99% relative to the benzene and 97% relative to the toluene, the 4.8 cubic meters/hour of extract containing only traces of nonaromatic hydrocarbons.

The extract fraction is subjected to water reflux distillation in a distillation column maintained at about C. at the head and at C. at the boiler.

The tail fraction is integrally recycled to the extraction column, loss of solvent by thermal decomposition does not exceed grams/ton of pure aromatics obtained after decantation of th head fraction.

I claim:

1. Process for the extraction and purification of aro- -matic hydrocarbon from a mixture of aromatic hydrocarbon and a member selected from the group consisting of aliphatic and naphthenic hydrocarbons, comprising the steps of (a) contacting the hydrocarbon mixture with a liquid solvent consisting essentially of water and a compound of the formula ROCSNH wherein R is alkyl of 1 to 6 carbons,

(b) separating a raflinate phase from an extract phase,

said extract phase comprising the solvent and aromatic hydrocarbon,

(c) distilling the aromatic hydrocarbon and water from said extract phase for subsequent further separation by settling and decanting, and

(d) water washing the raffinate phase whereby entrained solvent is separated therefrom.

2. Process of claim 1 wherein the liquid solvent consists essentially of water and methyl thiocarbamate.

3. Process for the extraction and purification of ammatic hydrocarbon from a mixture of aromatic hydrocarbon and a member selected from the group consisting of aliphatic and naphthenic hydrocarbons, comprising the steps of (a) contacting the hydrocarbon mixture With a liquid solvent consisting essentially of water, methyl carbamate and compound of the formula ROCSNH wherein R is alkyl of l to 6 carbons,

(b) separating a raflinate phase from an extract phase,

said extract phase comprising the solvent and aromatic hydrocarbon,

(c) distilling the aromatic hydrocarbon and Water from said extract phase for subsequent further separation by settling and decanting, and

(d) water washing the raffinate phase whereby entrained solvent is separated therefrom.

4. Process for the extraction and purification of aromatic hydrocarbon from a mixture of aromatic hydrocarbon and a member selected from the group consisting of aliphatic and naphthenic hydrocarbons, comprising the steps of (a) contacting the hydrocarbon mixture with a liquid solvent consisting essentially of from 5 to 15% Water and methyl car bamate,

(b) separating a raflinate phase from an extract phase,

said extract phase comprising the solvent and aromatic hydrocarbon,

(c) distilling the aromatic hydrocarbon and water from said extract phase for subsequent further separation by settling and decanting, and

(d) water washing the rafiinate phase whereby entrained solvent is separated therefrom.

References Cited by the Examiner DELBERT E. GANTZ, Primary Examiner. ALPHONSO D. SULLIVAN, Examiner.

C. E. SPRESSER, Assistant Examiner. 

1. PROCESS FOR THE EXTRACTION AND PURIFICATION OF AROMATIC HYDROCARBONFROM A MIXTURE OF AROMATIC HYDROCARBON AND A MEMBER SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC AND NAPHTHENIC HYDROCARBONS, COMPRISING THE STEPS OF (A) CONTACTING THE HYDROCARBON MIXTURE WITH A LIQUID SOLVENT CONSISTING ESSENTIALLY OF WATER AND A COMPOUND OF THE FORMULA ROCSNH2 WHEREIN R IS ALKYL OF 1 TO 6 CARBONS, (B) SEPARATING A RAFFINATE PHASE FROM AN EXTRACT PHASE, SAID EXTRACT PHASE COMPRISING THE SOLVENT AND AROMATIC HYDROCARBON, (C) DISTILLING THE AROMATIC HYDROCARBON AND WATER FROM SAID EXTRACT PHASE FOR SUBSEQUENT FURTHER SEPARATION BY SETTLING AND DECANTING, AND (D) WATER WASHING THE RAFFINATE PHASE WHEREBY ENTRAINED SOLVENT IS SEPARATED THEREFROM.
 3. PROCESS FOR THE EXTRACTION AND PURIFICATION OF AROMATIC HYDROCARBON FROM A MIXTURE OF AROMATIC HYDROCARBON AND A MEMBER SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC AND NAPHTHENIC HYDROCARBONS, COMPRISING THE STEPS OF (A) CONTACTING THE HYDROCARBON MIXTURE WITH A LIQUID SOLVENT CONSISTING ESSENTIALLY OFF WATER, METHYL CARBAMATE AND COMPOUND OF THE FORMULA ROCSNH2 WHEREIN R IS ALKYL OF 1 TO 6 CARBONS, (B) SEPARATING A RAFFINATE PHASE FROM AN EXTRACT PHASE, SAID EXTRACT PHASE COMPRISING THE SOLVENT AND AROMATIC HYDROCARBON, (C) DISTILLING THE AROMATIC HYDROCARBON AND WATER FROM SAID EXTRACT PHASE FROM SUBSEQUENT FURTHER SEPARATION BY SETTLING AND DECANTING, AND (D) WATER WASHING THE RAFFINATE PHASE WHEREBY ENTRAINED SOLVENT IS SEPARATED THEREFROM.
 4. PROCESS FOR THE EXTRACTION AND PURIFICATION OF AROMATIC HYDROCARBON FROM A MIXTURE OF AROMATIC HYDROCARBON AND A MEMBER SELECTED FROM THE GROUP COMPRISING OF ALIPHATIC AND NAPHTHENIC HYDROCARBONS, COMPRISING THE STEPS OF (A) CONTACTING THE HYDROCARBON MIXTURE WITH A LIQUID SOLVENT CONSISTING ESSENTIALLY OF FROM 5 TO 15% WATER AND METHYL CARBAMATE, (B) SEPARATING A RAFFINATE PHASE FROM AN EXTRACT PHASE, SAID EXTRACT PHASE COMPRISING THE SOLVENT AND AROMATIC HYDROCARTON, (C) DISTILLING THE AROMATIC HYDROCARBON AND WATER FROM SAID EXTRACT PHASE FOR SUBSEQUENT FURTHER SEPARATION BY SETTLING AND DECANTING, AND (D) WATER WASHING THE RAFFINATE PHASE WHEREBY ENTRAINED SOLVENT IS SEPARATED THEREFROM. 